Rotating objects have fascinated countless generations of children and adults, and one need not look far in the art to find numerous examples of toys whose operation incorporates a rotating element. The top, the flying saucer, the hula-hoop, and the yo-yo are but a few examples of such toys.
The key to a toy's long-term success is its ability to maintain the interest of the user as the user's dexterity and skill improve. This in effect presents a dual requirement on the toy. Unless a beginner can quickly master the rudiments of the toy's operation, he is likely to become discouraged and abandon efforts to perfect his skill. In such a case, the toy can scarcely be said to have universal appeal. Conversely, a toy that is capable of a limited number of maneuvers, or perhaps only simple maneuvers, fails to hold the interest of a user for more than a short period of time. To some extent, skill is correlated with age, and the most appealing toy is one that is capable of gratifying and challenging users of all ages. Every year, while numerous new toys enter the marketplace, the number of toys that have long-term appeal to people over a wide age range remains surprisingly small.